Conventionally, there has been provided a compressor including a disc-shaped screw rotor which rotates about a center axis and which has, in its end face in a center-axis direction, a plurality of spirally extending groove portions radially outward from the center axis, and a gate rotor which rotates about a center axis and which has a plurality of tooth portions arrayed circumferentially on its outer circumference, the groove portions of the screw rotor and the tooth portions of the gate rotor being engaged with each other to form a compression chamber (see JP 60-10161 B).
That is, this compressor is a so-called PP type single screw compressor. The term “PP type” means that the screw rotor is formed into a plate-like shape and moreover the gate rotor is formed into a plate-like shape.
Then, as viewed in a direction orthogonal to the screw rotor center axis and the gate rotor center axis, all the tooth portions of the gate rotor overlap with the screw rotor center axis. That is, the tooth portions of the gate rotor are engaged with the groove portions of the screw rotor along the radial direction of the screw rotor.
With a view to preventing interferences between the screw rotor and the gate rotor, side faces of the gate rotor tooth portions are given a maximum angle and a minimum angle each of which is formed by a gate rotor tooth-portion side face and a screw rotor groove wall surface on a plane which orthogonally intersects with the gate rotor plane and which contains a rotational direction of a tooth center line extending radial direction of the gate rotor (hereinafter, angles formed between the maximum angle and the minimum angle will be referred to as edge angles of the gate rotor; see edge angles δ1, δ2 of FIG. 20).